In the production of epoxysilicone compositions, transition metal catalysts have long been known to promote the hydrosilation reaction. See, for example, J. L. Speier, "Homogeneous Catalysis of Hydrosilation by Transition Metals", in Advances in Organometallic Chemistry, Vol. 17, pp. 407-447 (1979), F. G. A. Stone and R. West, eds., Academic Press (New York, San Francisco, London); Aylett, Organometallic Compounds, Vol. 1, John Wiley, New York 1979, p. 107; and Crivello and Lee, "The Synthesis, Characterization, and Photoinitiated Cationic Polymerization of Silicon-Containing Epoxy Resins", J. Polymer Sci., Vol. 28, John Wiley, New York 1990, pp. 479-503. Generally, the hydrosilation catalysts used are complexes of platinum, palladium, rhodium, iridium, iron or cobalt. In particular, platinum-containing catalysts have been widely used for this purpose.
However, it has been found that in addition to catalyzing the hydrosilation reaction between an ethylenically unsaturated epoxide and a silicon hydride, in the presence of silicon hydrides many transition-metal-complex hydrosilation catalysts also promote the oxirane ring-opening polymerization of the ethylenically unsaturated epoxide starting material and the epoxysilicone product of the hydrosilation reaction. Copending, commonly assigned Application serial no. 07/473,802 (Riding, et al.), filed February 2, 1990, discloses the use of platinum or platinum-based catalysts to promote the oxirane ring-opening polymerization of epoxides. This ring-opening polymerization reaction during production of an epoxysilicone is undesirable as the epoxide polymerization may cause the reaction mixture to gel completely, resulting in the loss of the entire batch and in loss of considerable time in cleanup of the insoluble gelled resin.
Additionally, a partial gelation due to the ring-opening polymerization reaction can occur during synthesis such that reproducible batch-to-batch viscosity of the epoxysilicone product is difficult to obtain. Such reproducibility in viscosity is highly preferred in the epoxysilicone industry, as these materials are typically used as coatings, for example release coatings, and the process of successfully and uniformly applying these coatings to PG,4 a substrate is highly dependent upon the viscosity of the coating material. Commonly assigned, copending applications to Eckberg, et al., U.S. patent application Ser. No. 802,679, filed Dec. 5, 1991, U.S. patent application Ser. Nos. 5,227,410 and 802,681, filed Dec. 5, 1991, disclose that viscosity control can be achieved by use of a tertiary amine stabilizer during the hydrosilation synthesis reaction. However, only certain catalysts are active in the presence of this stabilizer.
Furthermore, in the presence of precious metal hydrosilation catalysts, epoxysilicones have been found to slowly gel on storage at room temperature due to the epoxide ring-opening polymerization reaction, thus shortening the shelf-life of the epoxysilicone product. While this storage problem can be partially alleviated by deactivating the transition-metal-complex catalyst with an inhibitor of its catalytic activity, such as dodecyl mercaptan or 2-mercaptobenzothiazole in the case of platinum complexes, it would be preferable to not incorporate this extra component and additional process step into epoxysilicone composition and production process.
In order to minimize the oxirane ring-opening polymerization reaction, epoxysilicone fluids have been previously successfully produced only by careful control of batch temperature and olefin epoxide feed rate during the synthesis, followed by the above-mentioned inactivation of the catalyst after the completion of the hydrosilation reaction.
Certain hydrosilation catalysts containing phosphine ligands are known. For example, as disclosed by de Charentenay, F., Osborn, J. A., and Wilkinson, G., J. Chem. Soc. A. 1968, p.787, RhCl[(C.sub.6 H.sub.5).sub.3 P].sub.3 (Wilkinson's catalyst) efficiently catalyzes the hydrosilation reaction between SiH-containing silanes and siloxanes and vinyl epoxides. However, it was not previously known whether RhCl[(C.sub.6 H.sub.5).sub.3 P].sub.3 or other phosphine-containing catalysts also catalyze the epoxide ring-opening reaction described above.
As disclosed in commonly assigned U.S. patent application of Crivello and Fan, entitled "Preparation of Epoxysilicon Compounds using Rhodium Catalysts", U.S. Pat. No. 5,169,962 issued on Dec. 8, 1962 rhodium-based hydrosilation catalysts selectively promote the hydrosilation reaction without the promotion of an epoxide ring-opening polymerization reaction. A variety of epoxy-containing silicone monomers and oligomers can be synthesized using these catalysts. However, most of the catalysts traditionally used for synthesis of epoxysilicone compositions, particularly Pt-containing catalysts, do promote the epoxide ring-opening polymerization reaction, and therefore do not permit the selective hydrosilation synthesis of epoxysilicones.
There, therefore, exists a need in the epoxysilicone industry for a method of eliminating the oxirane ring-opening when employing commonly used hydrosilation catalysts. There also exists a need for an efficient yet economical method of producing epoxysilicone monomers and oligomers in the absence of the epoxide ring-opening side reaction, thereby producing epoxysilicone compositions of reproducible viscosity. There is additionally a need for epoxysilicone composition which is stable to the epoxide ring-opening reaction and, therefore, has an increased shelf-life without the additional step and cost of poisoning the catalyst after the completion of the hydrosilation addition reaction.
It is, thus, an object of the present invention to provide a method for preparing an epoxysilicone composition through the reaction between an ethylenically unsaturated epoxide and an organohydrogensilane or organohydrogensiloxane in the presence of a catalyst which efficiently promotes the hydrosilation reaction without also promoting the afore-mentioned oxirane ring-opening polymerization of either the ethylenically unsaturated epoxide starting material or the epoxysilicone product.
It is another object of the invention to provide a hydrosilation catalyst for the addition reaction between an olefin epoxide and a SiH-containing silane or siloxane to form an epoxysilicone compound, wherein the catalyst effectively promotes the hydrosilation reaction without also promoting the ring-opening polymerization of the epoxide ring in either the olefin epoxide starting material or the epoxysilicone product.
Still another object of the invention is to provide an epoxysilicone composition with reproducible batch-to-batch viscosity and enhanced storage life, and which is stable to oxirane ring-opening polymerization at room temperature.